I have a few very minor problems with my OS X install probably caused by my unprofessional tinkering with system files. I don't want to perform a clean installation at the moment and I also, please forgive me, don't currently have a time machine backup (I temporarily live abroad, am pretty much constantly on the move and I don't have any external drive with me). Can I just do the maintenance I think might help my computer by downloading Mountain Lion from the App Store and installing it over my current system - just as if I was doing an upgrade from a previous version of OS X, only I would be "upgrading" from the current version? Thanks a lot.